The present invention relates to a non-linear control arrangement for driving units in general, and more particularly to a control arrangement for use in printing machinery, such as the damping device driving unit control arrangement.
Especially in offset printing, the correct operation of the damping device has a considerable influence on the quality of the printed matter. Inasmuch as the consumption of the damping liquid depends to a high degree on the printing speed, the printing cylinder speed of rotation can be used as a guiding value in the automatic control of the driving arrangement of the damping device.
However, the relationships between the printing cylinder speed of rotation and the demand for the damping liquid, on the one hand, and between the damping duct roller speed of rotation and the amount of the damping liquid being fed thereby, on the other hand, are not linear. For this reason, is is necessary or at least advantageous to equip a control arrangement for the damping device with a circuitry which renders it possible to modify the input signal, which is representative of the speed of rotation of the printing cylinder, in such a manner as to obtain at the output of the control arrangement a control potential or voltage which is in the required non-linear relationship to the input signal that is needed for correctly controlling the damping device.
The need for such a non-linear control has already been recognized and a solution to this problem has been presented, for instance, in the Swiss Pat. No. 543,396. This patent discloses a damping device control arrangement for an offset printing machine wherein a resistance matrix is being used for the formation of non-linear functions. This resistance matrix converts a given mechanical signal, which is applied to the wiper of the input potentiometer, into an electrical output signal which varies in accordance with the adjustment of a plurality of connecting elements for rails which cross one another.
The input potentiometer is connected with the output potentiometer of this conventional matrix via the connecting elements in that the adjustable connecting elements themselves connect, via crossing rails, a plurality of vertical rails, which are electrically connected, at regularly spaced intervals, with the input potentiometer, with a corresponding plurality of horizontal rails which are electrically connected, at regularly spaced intervals, with the output potentiometer. The adjustment of the connecting elements is accomplished in such a manner that the electric output signal varies in accordance with a predetermined non-linear function.
The electrical connection of the rails with the potentiometers at regularly spaced intervals means that one connecting element is needed for each point of the respective interval of the curve to be simulated. This is true even if the slope of the curve is the same for a portion of the curve. This technical requirement for providing a separate connecting element for each point of the curve is reflected in the size and clarity of arrangement of the matrix. Any function values which are situated between the points that are determined by the construction of the particular matrix can be represented only if the matrix is expanded. For achieving accurate simulations of the individual curve sections, even the remaining part of the matrix must be made correspondingly large.
Thus, it may be seen that the above-discussed resistance matrix is disadvantageous in several respects in that it permits the achievement of an accurate simulation of the functional relationships between the aforementioned factors only at the expense of a substantial cost, diminishment of the clarity of arrangement, and increase in the amount of available space which must be set aside for the resistor matrix. In addition thereto, the adjustment or the operation of the arrangements of this type is quite complicated.